1. Field of Invention
The present disclosure relates to a phosphorous-containing phenol-formaldehyde novolac structure and the preparation method thereof, and the use of the compound to react with the epoxy group of an epoxy resin to obtain an environmentally-friendly and high performing halogen-free cured flame retarding epoxy resin.
2. Description of Related Art
The chemical structure of epoxy resin features its desirable properties, e.g., reactivity, toughness, flexibility, good mechanical properties, electrical properties, dimensional stability, and superior bonding properties for different substrates. The cured epoxy resin can not only maintain the original features of the substrate, but also further block out water, gas and chemicals, and it is also lightweight and low cost. Therefore, epoxy resin is widely used in electronics and aerospace industries, especially in the field of semiconductor packaging material, printed circuit board substrate material and so on. However, when the epoxy resin is applied to a printed circuit board, there is a lack of flame retarding. In the past, halogen based flame-retardant was added to the epoxy resin to meet the flame-retarding requirements. The halogen based flame-retardant will produce dioxin, benzofuran and other irritating and corrosive harmful gases when burnt, and the small molecules of the flame-retardant often cause a reduction in the mechanical properties and will photodecompose, thus causing material deterioration. At the same time, there will be migration and volatility issues, resulting in a reduction of the material performance and the flame-retarding effect is not ideal. Therefore, the use of organic phosphorus compound flame-retardants in thermosetting epoxy resin compositions instead of halogenated flame-retardants is constantly emerging, for example, in patents such as EP A 0384939, EP A 0384940, EP A 0408990, DE A 4308184, DE A 4308185, DE A 4308187, WO A 96/07685, and WO A 96/07686. In addition, for the printed circuit laminates, with the rise of environmental awareness, the current international norms require lead free processes, therefore the processing of the substrate are now more demanding, especially regarding the vitrification temperature (Tg) of the material and the heat resistance of the substrate in a tin furnace has become an important issue that researchers in this field must overcome.